Abstract
A new approach is proposed for the selection of reagent ion species in a gas chromatography-chemical ionization mass spectrometry (GC-PICI-MS) method for GBL and 1,4-BD determination, the two “prodrugs” of gamma-hydroxybutyric acid (GHB), a drug associated with sexual assault. The GC-PICI-MS is often the best technique to avoid an extended fragmentation occurring in EI source and it preserves the information on molecular ions. Ion-trap mass spectrometry (IT-MS) is a valuable tool in chemical ionization experiments, commonly affording reaction times 104–105 higher than those in conventional CI sources. This feature allows the use of either vapors from liquid reagents, or many reactant species that are difficult to generate and employ in the conventional CI experiments. In this research acetone, acetonitrile, methanol and diethylamine were evaluated to generate vapors of the chemical ionization species. The use of liquid CI reagent offers a wide range of chemical–physical properties that can greatly affect the specificity, with the possibility to modulate the detection of the analyte in comparison with background or matrix interferences. The experimental data using different CI liquid reagents and reaction times were compared through calibration curves of GBL and 1,4-BD (ranging from 10 to 1000ng/mL). The linear regression curves obtained were used to calculate the sensitivity (slope) and limit of detection (LOD) of the method. Methanol resulted in the most efficient reagent for the determination of studied analytes. However, its employment as ionization agent of the 1,4-BD favors the hydride abstraction mechanism or hydrogen loss from protonated-molecule ions. These phenomena can be considered as a possible sources of uncertainty or errors. Therefore, acetonitrile can be employed as a good compromise between sensitivity and reliability of signal for both analytes.
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